Acid copper chromate (ACC) wood preservatives are required by the American Wood Preservers Association Standard to have 31.8-28.0% copper as CuO and 68.2-63.3% hexavalent chromium as CrO.sub.3. In addition, water soluble compounds used to make up the preservative must be bivalent copper, e.g. copper sulfate and hexavalent chromium, e.g. sodium or potassium dichromate and chromium trioxide.
ACC compositions are traditionally formulated with copper sulfate which is only moderately water soluble. Thus it is not feasible to form concentrates with copper sulfate containing formulations so as to obviate shipping excess water.
Accordingly, it is the object of this invention to provide novel wood preservatives which meet the AWPA Standard for ACC compositions but also can be formed in concentrates having from 25 to 60% total CuO and CrO.sub.3 oxides. In addition, formulations are provided which, when diluted to the 0.8 to 14% level for application to wood, not only have the correct oxide ratio of from 1 part CuO to 2.145 CrO.sub.3 to 1 part CuO to 2.161 CrO.sub.3, but also have the proper pH of from 2.0 to 3.9 at 68.degree.-77.degree. F. when diluted to an aqueous solution of 15 to 22 grams of oxide per liter.
In contrast thereto, a liquid concentrate with copper sulfate and sodium dichromate dihydrate requires a reduction in total oxide content to 18% by weight for solubility down to 38.degree. F.